Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$55.56	7.149%	$59.532	$59.53	$59.55	$59.50
Purchase #2	$224.76	10.157%	$247.5889	$247.59	$247.60	$247.60
Purchase #3	$113.40	13.346%	$128.5344	$128.53	$128.55	$128.50
Purchase #4	$122.84	12.483%	$138.1741	$138.17	$138.15	$138.20
Purchase #5	$177.41	5.810%	$187.7175	$187.72	$187.70	$187.70
Purchase #6	$89.99	6.378%	$95.7296	$95.73	$95.75	$95.70
Purchase #7	$138.30	4.857%	$145.0172	$145.02	$145.00	$145.00
7 purchase totals =	$922.26		$1,002.2937	$1,002.29	$1,002.30	$1,002.20